1901 - 2 .] 
J. G. Goodchild on Scottish Mineralogy. 
331 
and formed the assemblage of minerals which usually occurs in 
calcareous rocks under these circumstances. Speaking generally, 
these, in Scotland, usually include Quartz, Tremolite, Diopside, 
Phlogopite, Andesine, Anorthite, Spinel, Wollastonite, Graphite, 
Sphene, Pyrrhotine, the variety of Garnet known as Cinnamon 
stone, together with Tdocrase, and often with Zoisite, Spodumene, 
and others. Latterly Brucite has been detected in one of the 
Scottish marbles. Many of these minerals, and especially the six 
mentioned first, are closely related to the original constituents of 
eruptive rocks. Hence it may be concluded that these latter rock- 
forming minerals themselves may really he, like those developed 
by metamorphic action within the marble, also of hydrothermal 
origin, as so many observers have from long since maintained. 
Olivine has not yet been observed to have been formed in this 
way. But the mineral under notice, Forsterite, which is an 
Orthorhombic Magnesium Orthosilicate, is very closely allied in 
both composition and crystalline habit to Olivine, and has indeed 
often been termed White Olivine. Since Mr Teall’s paper appeared 
I have made a careful examination of other Scottish marbles 
whose history had been much the same as that of Glenelg. One 
set of specimens of metamorphosed Durness (Cambrian) dolomitic 
limestone, from Ledbeg, in Sutherlandshire, showed on a weathered 
surface a large number of crystals of this magnesium silicate. 
It had been placed with Diopside, and appears to have been 
figured as that species. Other examples of the same mineral in the 
Collection had been regarded as Chondrodite, Totaigite, etc. Some 
crystals were forthwith detached from the matrix, mounted on 
small corks as usual, and then examined with the goniometer. 
The faces were too dull to give more than rough approximation, 
but these agreed with Forsterite. As this mineral has rarely been 
figured, I give two characteristic examples here (figs. 4 and 5). The 
crystals are all attached by the c {001} axis; and they are all 
flattened parallel to b {010}. Their general habit is rhomboidal. 
The forms shown are the following : — 
The Brachypinacoid, b {010} ; the Unit Prism, m {110} ; the 
Unit Pyramid, e {111} ; the Brachydome, k {021}; and the 
Brachypyramid, Z {131}. The registration numbers of the 
specimens figured are 375/7 and 375/8. It may he observed 
